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SMHS Higher Physics > Electricity > Flashcards

Electricity Flashcards

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1
Q

State what is meant by an alternating current

A

a.c. is a current which changes direction and instantaneous value with time.

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2
Q

How do you determine the peak voltage from an oscilloscope?

A

Vpeak = number of divisions X y gain

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3
Q

State what is meant by a direct current

A

d.c. is a current that does not change direction or instantaneous value with time.

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4
Q

Sketch a graph of current vs time for a discharging capacitor

A

Discharging capacitor graph current vs time

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5
Q

Describe the effect of changing resistance on the charging and discharging curves for a capacitor?

A

Increasing resistance increases discharge time

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6
Q

State what is meant by the short circuit current

A

The current drawn from a supply when the terminals are connected together with no load resistance. This can produce a large current and can be dangerous.
I = E/r

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7
Q

What is a p-n junction?

A

A p-n junction is an interface or a boundary between two semiconductor material types, namely the p-type and the n-type, inside a semiconductor. The p-side or the positive side of the semiconductor has an excess of holes and the n-side or the negative side has an excess of electrons.

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8
Q

Describe experiments to measure the current and voltage for charging and discharging capacitors

A

A = Discharging B = charging
Measure the current and voltage at regular intervals using the voltmeter and ammeter

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9
Q

What are the rules for a parallel circuit?

A

Is = I1 + I2… (splits at branches)
Vs=V1 =V2 =……
1/RT = 1/R1 + 1/R2 + …..

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10
Q

State the difference between and intrinsic and extrinsic semiconductor?

A 
Intrinsic = pure semiconductor
Extrinsic = impurities atoms have been added
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11
Q

What is internal resistance?

A

Charges passing through a cell meet resistance. A cell therefore has internal resistance.

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12
Q

How do you find the EMF and short circuit current from the graph?

A

EMF = y intercept
Short circuit current = x intercept

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13
Q

State what is meant by lost volts

A

Vlost = Ir
The voltage across the internal resistance when a load resistance is connected.

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14
Q

Describe an experiment to find the EMF and internal resistance of a supply.

A

Adjust variable resistor and take readings of V and I.
Plot a graph of V against I. Gradient of graph = -r.
OR
measure the voltage E when switch open. Close the switch and take a reading of V and I.
Calculate r using E = V + Ir

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15
Q

State the two types of conduction in semiconductors?

A

Electrons moving in the conduction band Holes moving in the partially filled valence band

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15
Q

State the two types of conduction in semiconductors?

A

Electrons moving in the conduction band Holes moving in the partially filled valence band

16
Q

Which equations are used for potential divider circuits?

A 
V1 = (R1/ R1 + R2) x Vs
V1/V2 = R1/R2
17
Q

State what is meant by terminal potential difference (TPD)

A

Vtpd = E- Ir
The energy per coulomb
transferred by a supply when a load resistance is connected.

18
Q

How are peak and rms values related?

A

Vrms = Vpeak/√2

Irms = Ipeak/√2

19
Q

What is Ohm’s Law?

A

V=IR

20
Q

What is forward bias?

A

Forward biasing means putting a voltage across a diode that allows current to flow easily

• Current flows • Depletion
zone narrows

21
Q

Describe the band structure of insulators, semiconductors and conductors

A

The band gap in conductors overlaps. The band gap in semi conductors is small. The band gap in insulators is large.

22
Q

State what is meant by E - the electromotive force (EMF)

A

The total amount of energy given to each coulomb of charge by a power supply.

23
Q

What do the symbols mean? What are their units? Q=It

A

Q = Charge - measured in coulombs (C)

I = Current - measured in amperes (A)

t = time - measured in seconds (s)

24
Q

Describe how an n-type semiconductor is formed

A

A material such as silicon has impurities added with an extra outer electron e.g. Arsenic

25
Q

How do you find the internal resistance from the graph

A

The magnitude of the gradient

26
Q

What is reverse bias?

A

reverse biasing means putting a voltage across a diode in the opposite direction. The voltage with reverse biasing doesn’t cause any appreciable current to flow. This is useful for changing AC current to DC current.

No current • Depletion
zone widens

27
Q

Silicon can be doped with arsenic to produce an n-type semiconductor.
State the effect that doping has on the conductivity of silicon.

A

Increases conductivity.

28
Q

How do you calculate electrical power?

A

P = IV = I2R = V2/R
USING RMS VALUES

29
Q

How do you determine the frequency from an oscilloscope?

A

T = divisions x timebase frequency = 1/𝑇
Remember: ms = miliseconds

30
Q

Describe how a p-type semiconductor is formed

A

A material such as silicon has impurities added with one fewer extra outer electron e.g. Indium

31
Q

State what is meant by a capacitance of 1F

A

1F means one coulomb of charge stored per volt

32
Q

What are the rules for a series circuit?

A 
Is = I1 = I2...... 
Vs = V1 +V2 + ...... 
RT = R1 + R2 + ......
33
Q

Explain what is meant by a photovoltaic effect

A
  • Photons are absorbed when electrons move from the valence band to the conduction band.
  • The p-n junction causes the electrons in the conduction band to move towards the n-type semiconductor
  • A potential difference is produced across the junction
34
Q

C = Q/V
What is meant by the symbols
What are their units

A

C= capacitance(F)
Q= Charge(c)
V=Voltage/Potential Difference(V)

35
Q

Explain why the reading on the voltmeter decreases when the switch is closed

A

There is a current flowing when the switch is closed and voltage is lost across the internal resistor.

36
Q

Which equations do you use to find the energy stored by a capacitor.

A

E=1/2 QV = 1/2 CV² = 1/2 Q²/C

SMHS Higher Physics (4 decks)

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